Zig

MIME Body vs. Sub-Parts

See more MIME Examples

Explains the difference between sub-parts and body.

MIME documents (i.e. messages) can have a nested structure. The simplest MIME message contains a header followed by content (possibly encoded). The header is delimited from the content by two consecutive CRLF's.

A MIME message may be multipart. If so, then the Content-Type header field indicates "multipart" and the content the follows the header is itself a MIME message, which may also be multipart, etc. You can see how MIME messages effectively have a tree structure. The non-leaf nodes have Content-Types that are "multipart/" and the leaf nodes have non-multipart Content-Types.

The Chilkat MIME component/library uses two terms that need to be understood in order to effectively use the API. These are "body" and "sub-part". A multipart node has 1 or more sub-parts, but its body is empty. A leaf node (i.e. non-multipart node) has no sub-parts, but the body is (usually) non-empty.

This example creates a multipart MIME message and shows the results of getting the sub-parts and body of each node.

Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    const mime = try chilkat.Mime.init();
    defer mime.deinit();

    // Create a multipart/mixed MIME message with two sub-parts.
    // We'll use the Base64 encoding for the 2nd sub-part.
    const part1 = try chilkat.Mime.init();
    defer part1.deinit();
    try part1.setBodyFromPlainText("This is part 1");

    const part2 = try chilkat.Mime.init();
    defer part2.deinit();
    try part2.setBodyFromPlainText("This is part 2");
    part2.setEncoding("base64");

    try mime.newMultipartMixed();
    mime.setUseMmDescription(false);
    try mime.appendPart(part1);
    try mime.appendPart(part2);

    // Show the MIME message:
    std.debug.print("{s}\n", .{try mime.getMime(alloc)});

    // Here's the MIME:
    // Content-Type: multipart/mixed;
    //     boundary="------------040605030407000302060008";
    //
    // --------------040605030407000302060008
    // Content-Type: text/plain;
    //      charset="us-ascii";
    // Content-Transfer-Encoding: 7bit
    //
    // This is part 1
    // --------------040605030407000302060008
    // Content-Type: text/plain;
    //      charset="us-ascii";
    // Content-Transfer-Encoding: base64
    //
    // VGhpcyBpcyBwYXJ0IDI=
    //
    // --------------040605030407000302060008--

    // If we examine the root node of the MIME message,
    // we see that it has 2 sub-parts and the body is empty (as expected)
    const n = mime.getNumParts();
    std.debug.print("Num Parts = {d}\n", .{n});
    std.debug.print("Body = {s}\n", .{try mime.getBodyDecoded(alloc)});

    // The GetEntireBody retrieves the entire content after
    // the header.  (Perhaps GetEntireBody should've been named
    // GetEntireContent to make it less confusing...)
    std.debug.print("---- EntireBody:\n", .{});
    std.debug.print("{s}\n", .{try mime.getEntireBody(alloc)});
    std.debug.print("********\n", .{});

    // Now examine the 2nd sub-part.  It has a body encoded
    // using base64.  Get the contents of the body in both
    // decoded and encoded forms:

    // index 0 is the 1st part, index 1 is the 2nd part.
    const part = try chilkat.Mime.init();
    defer part.deinit();
    mime.partAt(1, part) catch {};

    std.debug.print("Decoded Body:\n", .{});
    std.debug.print("{s}\n", .{try part.getBodyDecoded(alloc)});
    std.debug.print("Encoded Body:\n", .{});
    std.debug.print("{s}\n", .{try part.getBodyEncoded(alloc)});
}